Thread: any issue with enable_partitionwise_join at instance level?

Hello, while running aggregate queries on partitioned table there is improvement when enable_partitionwise_join is turned on. By default this parameter is disabled and going by the documentation it says (https://www.postgresql.org/docs/11/runtime-config-query.html)

```
Because partitionwise grouping or aggregation can use significantly more CPU time and memory during planning, the default is off.
```

Why would it take "significantly" more CPU and memory for the planner? Is there any foreseeable issues when enabling this at the instance level?